This invention relates to an improved apparatus and process for stretching a tow of filaments by tension on the tow caused by driven rolls dragging the tow across drag rolls. The improvement comprises continuously controlling at least one undriven roll proportional to a sensed variation in a ratio of speed between at least one driven roll and at least one drag or undriven roll. The tow stretching apparatus of the prior art is described in U.S. Pat. No. 3,266,082 to Brandi, hereby incorporated by reference in toto. See also U.S. Pat. No. 3,422,492 to Gorecki, pertinent portions of which are hereby incorporated by reference.
Fiber processed by the prior art process and apparatus lacks uniformity in denier, elongation, tenacity, and crimps per inch. These parameters must be uniform, particularly with certain spinning machinery used to spin the staple fiber to yarn. Also non-uniformity in these products creates streaks in dyed fabrics such as carpet.
The prior art apparatus for stretching a tow of filaments comprises travelling the tow serially through drag rolls and driven rolls with the tow being stretched by the tension on the tow caused by the driven rolls dragging the tow across the drag rolls with at least one of the drag rolls being braked or locked. Also a nip roll stand can precede the drag rolls with driven crimper feed rolls, driven crimper nip rolls, and a crimper box in series subsequent to the driven rolls. The prior art has means to drive the driven rolls, crimper feed rolls and crimper nip rolls, means to selectively lock (to prevent rotation) or brake at least one of the drag rolls and means to mount the rolls and crimper box. A single means such as an electric motor can be used to drive all the driven rolls, crimper feed rolls and crimper nip rolls. The prior art process is for stretching a tow of filaments by tension on the tow caused by driven rolls dragging the tow across a braked or locked drag roll. Fluctuations in the pretension at the nip roll stand have caused significant non-uniformity in drawn fiber denier, elongation, and tenacity.